1. Field of the Invention
The present invention is a polyester resin, a method for its preparation, a method for manufacturing at increased productivity therefrom a dimensionally stable polyester yarn having a low fray count, and the yarn thereby produced. The polyester resin is prepared from high purity terephthalic acid having a particle size distribution described by a Weibull function with narrow ranges of characteristic size and shape factor. The polyester yarn is useful for tires, industrial products and other applications.
2. Description of the Related Art
The production of polyester yarns is a continually evolving art. Global competition generates need for higher productivity processes and superior products. These needs are particularly manifested in the area of reinforcing yarns for automotive tires where trends toward larger vehicles and greater highway speeds present challenges to tire design and manufacture.
The preparation of linear polyesters by direct polymerization of terephthalic acid and glycols is well known. The prototypical polyester is poly(ethylene terephthalate) although other polyesters are both known and useful. Both batch and continuous processes for direct polymerization have been described. Batch processes have been described for example in U.S. Pat. No. 2,465,319 to Whinfield et al.; U.S. Pat. No. 3,050,533 to Munro et al.; U.S. Pat. No. 3,842,041 to Browne et al.; U.S. Pat. No. 4,077,945 to Heinze et al.; British Patent GB 1,387,759 to Browne et. al.; and Japanese Patents JP 56050731 B4 to Kamatani et al.; and JP 52126498 A2 to Murada et al.
Continuous processes have been described for example in U.S. Pat. No. 3,390,135 to Seiner; U.S. Pat. No. 3,590,072 to Leybourne III; U.S. Pat. No. 3,655,729 to Rinehart; U.S. Pat. No. 3,689,461 and U.S. Pat. No. 3,697,579 to Balint et al.; U.S. Pat. No. 3,892,798 to Heeg et al.; U.S. Pat. No. 4,001,187 to Itabashi et al.; U.S. Pat. No. 4,039,515 to Rebhan et al.; U.S. Pat. No. 4,096,124 to Wu et al.; U.S. Pat. No. 4,100,142 to Schaefer et al.; U.S. Pat. No. 4,110,316 to Edging et al.; U.S. Pat. No. 4,382,139 to Kapteina et al.; and British Patent GB 1,296,242. The publication by Hummel et al., xe2x80x9cContinuous Preparation of Polyester Fibers from Dimethyl Terepthalate or Pure Terephthalic Acidxe2x80x9d, Chem. Ind., 21, 251-4 (1969) describes a continuous polyester process with direct spinning.
In a typical direct polymerization process, terephthalic acid and glycol are mixed together and fed to a reactor as a slurry or a paste. The particle size and/or the particle size distribution of the terephthalic acid has been given repeated consideration for its effect on the viscosity of the terephthalic acid/glycol slurry or paste. Low slurry/paste viscosities are preferred but widely divergent methods have been employed to achieve this objective with equally divergent conclusions. In what follows, the terms micrometers and microns (symbol: xcexc) will be understood to be the same unit, namely one-millionth of a meter.
U.S. Pat. No. 3,431,243 to Uno et al. teaches compressing terephthalic acid to produce particles not more than 8 mm (8000 micrometers) in size.
U.S. Pat. No. 3,655,729 to Rinehart teaches use of terephthalic acid having from 40 to 90 wt % of particles larger than 420 microns but smaller than 869 microns and from 10 to 60 wt. % of particles smaller than 420 microns of which the major portion is smaller than 149 microns.
U.S. Pat. No. 4,100,142 to Schaefer et al. teaches use of terephthalic acid particles having a normal distribution of sizes within the range 15 to 50 microns and having particles larger than 100 microns removed by screening. Alternatively, a bi-modal distribution is described with a major peak in the range of 7 to 15 microns and a minor peak in the range of 80 to 120 microns.
U.S. Pat. No. 4,382,139 to Kapteina et al. teaches use of terephthalic acid crushed into very fine particles in the molecular disperse size range.
U.S. Pat. No. 4,334,090 to Donaldson teaches attrition of terephthalic acid crystals before forming a slurry. No particular particle size range is specified.
Japanese Patent JP 3071556 B2 to Nakoa et al. teaches terephthalic acid particle sizes less than 100 micron.
Japanese Patent JP 52126498 A2 to Murada et al. teaches terephthalic acid particles with a Stokes diameter uniformity less than 1.6. Examples of the invention included median particle sizes from 63 to 95 microns. Comparative examples ranged in median particle size from 71 to 145 microns.
Japanese Patent JP 56050731 B4 to Kamatani et al. teaches a terephthalic acid median particle size less than 300 microns with less than 20 wt % of particles larger than 500 microns. Examples of the invention included median particle sizes from 25 to 250 microns with 0.5 to 10 wt % of particles larger than 500 microns. Comparative examples ranged in median particle size from 50 to 100 microns with 1 to 6 wt % of particles larger than 500 microns.
German Patent DE 2 023 709 to Leybourne teaches a terephthalic acid particle size distribution such that at least 10% of the particles are retained on a 165-297 micron screen and at least 10% pass through 63 micron screen.
However, of this group of patents in which terephthalic acid particle size has been considered, only one, U.S. Pat. No. 4,100,142 describes polyester of fiber forming quality and high molecular weight, i.e., intrinsic viscosity greater than 0.8. Moreover, no connection has heretofore been made between the particle size distribution of the terephthalic acid employed in forming a polyester, and the productivity of the process of preparing a yarn from that polyester.
Processes for the preparation of polyester yarns have been described for example in U.S. Pat. Nos. 4,851,172 to Rowan et al.; U.S. Pat. Nos. 4,867,936 and 4,975,326 to Buyalos et al.; U.S. Pat. Nos. 5,067,538, 5,234,764 and 5,630,976 to Nelson et al.; U.S. Pat. No. 5,266,255 to Gibbon et al.; U.S. Pat. No. 5,741,587 to Bennie et al.; and U.S. Pat. No. 6,287,688 to Howell et al. U.S. Pat. Nos. 5,067,538, 5,234,764, and 5,630,976 disclosing dimensionally stable polyester yarns are particularly relevant to the present invention and are hereby incorporated herein by reference to the extent not incompatible herewith.
Dimensionally stable polyester yarns are prepared by spinning high molecular weight polyester of intrinsic viscosity at least about 0.8 under high stress conditions and then hot drawing to near the breaking point. During spinning and drawing at high stress, it is not uncommon for individual filaments in a yarn bundle to break forming xe2x80x9cslubsxe2x80x9d or xe2x80x9cfraysxe2x80x9d. Frays are obviously undesirable but not necessarily fatal to the use of the yarn so long as the tensile strength of the yarn bundle is maintained within stringent standards. However, when the number of frays is excessive, then stringent yarn tensile specifications cannot be met, product is scrapped, and productivity falls. Indeed, when the number of frays is excessive, the yarn may completely break in the spinning or drawing operation. This necessitates re-stringing the line with attendant and costly downtime. A need exists to identify and to eliminate, to the degree possible, all sources of frays. This has been a long felt but unsatisfied need, although the means for its amelioration have long been available.
The invention provides a polyester resin, a method for its preparation, the polyester resin prepared by the method of the invention, a method of manufacturing therefrom a dimensionally stable, high molecular weight polyester yarn at increased productivity and reduced fray count, and the yarn thereby produced.
The polyester resin has an intrinsic viscosity of at least about 0.8 dl/g measured in a 60/40 (w/w) mixture of phenol/tetrachloroethane at 25xc2x0 C. and has a filter-blinding index less than about 10,000 Pa-cm2/g measured at a throughput of 1.25 g/min of melt flow per cm2 of filter area for 244 minutes at 300xc2x0 C. through a 128xc3x97905 mesh/cm twilled Dutch weave screen having apertures less than 8 microns in dimension.
The method of preparing the polyester resin comprises the steps of: selecting a high purity terephthalic acid having a particle size distribution described by a Weibull function with an index of determination of 0.990 or greater, said distribution having a characteristic size from about 100 to about 140 micrometers and a shape factor from about 1.5 to about 2.1; reacting the terephthalic acid with a glycol and polymerizing to form a linear polyester having an intrinsic viscosity of at least about 0.8 dl/g measured in a 60/40 (w/w) mixture of phenol/tetrachloroethane at 25xc2x0 C.
The invention also includes as an embodiment the polyester resin prepared by the method of the invention.
The method of manufacturing the dimensionally stable polyester yarn comprises the steps of: selecting a high purity terephthalic acid having a particle size distribution described by a Weibull function with an index of determination of 0.990 or greater, said distribution having a characteristic size from about 100 to about 140 micrometers and a shape factor from about 1.5 to about 2.1; reacting the terephthalic acid with a glycol and polymerizing to form a linear polyester having an intrinsic viscosity of at least about 0.8 dl/g measured in a 60/40 (w/w) mixture of phenol/tetrachloroethane at 25xc2x0 C.; extruding the polyester through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn; withdrawing and solidifying the molten spun yarn at sufficient speed to form a crystalline, partially oriented yarn; and hot drawing the yarn to a total draw ratio of about 1.5:1 to about 3:1.
The invention also includes as an embodiment the dimensionally stable yarn prepared by the method of the invention. The yarn of the invention is useful for tires, industrial products and other applications.